Which of the following is not a reason why stis spread so quickly?
a.
many people with stis are asymptomatic.
b.
negative stigmas prevent people from seeking .
c.
protection used during sex usually fails.
d.
many people have a false sense of invulnerability.

Describe the potential effects, on people, of unprotected exposure to the sun.give an example of 1 new thing have you learned about the sun’s uv rays.

Which of the following is a health risk associated with ground-level ozone? a.cataractsb.skin cancerc.respiratory illnessd.all of the above

[120 total points] (public health) in one of the largest human experiments ever conducted, in 1954 a randomized controlled trial was run to see whether a vaccine developed by a doctor named jonas salk was effective in preventing paralytic polio. a total of 401,974 children (ages 6–9), chosen to be representative of those who might be susceptible to the disease, were randomized to two groups: 200,745 children (the control group c) were injected with a harmless saline solution (a placebo) and the other 201,229 children (the treatment group t) were injected with salk’s vaccine.what was the point of giving saline solution to the children who didn’t get the vaccine? explain briefly.